Adaptive electrical capacitance volume tomography

ABSTRACT

An electrical capacitance tomography sensor including a sensor having a plurality of electrodes, where each electrode is formed from a plurality of capacitance segments. Each of the capacitance segments of each electrode can be individually addressed to focus the electric field intensity or sensitivity to desired regions of the electrodes and the sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. application Ser. No.13/644,973, filed Oct. 4, 2012, which claims the benefit of U.S.Provisional Patent Application No. 61/543,233, filed Oct. 4, 2011, bothof which are hereby incorporated by reference in their entirety as iffully recited herein.

BACKGROUND OF THE INVENTIVE FIELD

The present invention is directed to process tomography and, inparticular, to an electrical capacitance volume tomography (ECVT) systemand using an adaptive capacitance sensor that allows focusing of theimaging region, increasing of volume image resolution, and steering ofthe electric field direction toward the region of interest.

Dynamic ECVT is a technology that senses measured capacitances between asensor region to generate a whole volume image of the region. ECVTtechnology has been applied in providing imaging of objects movingthrough a pipe for example. ECVT has provided insights into multiphaseflow phenomena in many industrial processes often in a combination ofgas, liquid, and solid states, including pneumatic conveying, oil pipelines, fluidized beds, bubble columns and many other chemical andbiochemical processes. It may also be used for imaging biologicalprocesses and tissues.

An ECVT system is generally made up of a sensor, sensor electronics anda computer system for reconstruction of the image sensed by the sensor.An ECVT sensor is generally comprised of n electrodes or plates placedaround a region of interest, in one embodiment providing n(n−1)/2independent mutual capacitance measurements which are used for imagereconstruction. Image reconstruction is performed by collectingcapacitance data from the electrodes placed around the wall outside thevessel.

Further details regarding the theory and application of ECVT, sensordesign, image reconstruction, and deployment of an ECVT system are foundin the U.S. Patent Application Publication No. U.S. 2010/0097374 (U.S.patent application Ser. No. 11/909,548), the relevant disclosures ofwhich are included by reference thereto as if fully set forth herein.

The present invention addresses resolution issues present withtraditional ECVT technology. More particularly, the present inventionaddresses various factors that limit ECVT resolution, including:

-   -   The limited number of capacitance plates, and arrangements        thereof, that can be used;    -   Limited sensitivity matrix produced from an uneven distribution        of electric field intensity between different plate        combinations;    -   Ill-conditioned system that makes the system more sensitive to        noise at sections of the imaging domain compared to others;    -   Soft field nature of ECVT that is a consequence of the electric        field changing its distribution inside the imaging domain based        on change of material distribution; and    -   the inability to focus the sensors to a particular region of the        imaging domain to allow for more focused reconstructed imaging;    -   the ill-posed inverse problem inherit in ECVT, which is a result        of attempting to reconstruct a number of voxels that is much        higher than measured data (i.e., less independent equations with        more unknowns);    -   the limited number of independent capacitance measurements used        to reconstruct a volume image;    -   the minimum required capacitance plate size that restricts scale        of region being imaged;    -   the limited length of capacitance sensor restricted by maximum        distance between plates and minimum size of each plate in an        ECVT sensor;    -   the lack of flexibility in applying different voltage signals        simultaneously to address different imaging applications.

The present invention is based on an adaptive capacitor sensor array,and associated sensor electronic circuit, that allows focusing of theimaging region and the steering of the electric field direction towardthe region of interest. It also allows for higher imaging resolution,increased number of independent capacitance measurements, and relaxationof sensor size limitations.

SUMMARY OF THE GENERAL INVENTIVE CONCEPT

In the preferred embodiment, the ECVT electrodes are comprised of anarray of smaller capacitance segments that may be individuallyaddressed. For example, each segment may be activated with differentamplitudes, phase shifts, or frequency to provide the desiredsensitivity matrix distribution. In one embodiment, the array ofselected capacitance segments can form many pairs of capacitanceelectrodes or plates without reducing overall plate size. Thecapacitance segments can also be joined in different configurations toprovide different designs. The term “envelope” refers to the shape ofdifferent voltage amplitudes on segments of one plate. Excitationfrequency is the frequency of the signal applied to each segment.

The sensor electronics of the present invention is designed to detectand measure the capacitance for the adaptive ECVT sensor of the presentinvention. For example, the difference in electrical energy stored inthe adaptive ECVT sensor would be measured between an empty state and astate where an object is introduced into the imaging domain (e.g.,between the electrodes). In a preferred embodiment of the invention, theterm “adaptive” means the ability to provide selective or highresolution control through the application of voltage or voltagedistributions to a plate having an array of capacitance segments. Thechange in overall energy of the system due to the introduction of adielectric material in the imaging domain is used to calculate thechange in capacitance related to the dielectric material. The change incapacitance can be calculated from the change in stored energy. Sensorelectronics can also be designed by placing individual segment circuitsin parallel yielding a summation of currents representing totalcapacitance between segments under interrogation. By individuallyaddressing the capacitance segments of the electrodes of the presentinvention, electric field distribution inside the imaging domain can becontrolled to provide the desired sensitivity matrix, focus the electricfield, and increase overall resolution of reconstructed images. Voltagedistribution can also be achieved by using a conventional measuringcircuit with a sensor that distributes voltages through a voltagedivider.

Tomography system based on adaptive sensors technology can be used inmany different industrial and medical applications. Examples ofindustries that can utilize developed technology are energy,pharmaceutical, chemical, aerospace, petrochemical, process engineering,healthcare, and multi-phase flow industries. In one example embodimentof the invention, the sensor for use in an electrical capacitancetomography system, is comprised of: a first electrode comprised of aplurality of capacitance segments; a second electrode spaced apart fromthe first electrode, the second electrode comprised of a plurality ofcapacitance segments; where the plurality of capacitance segments of thefirst electrode are individually addressable with voltages; where thecapacitance segments of the first electrode form capacitors withcorresponding capacitance segments of the second electrode; and wherethe second electrode is connected to a measuring circuit and wherein thecapacitors induce currents in the measuring circuit when charged, thecurrent used to obtain capacitance levels of the capacitors.

The sensor may also be comprised of: a third electrode comprised of aplurality of capacitance segments; a fourth electrode comprised of aplurality of capacitance segments; where the first, second, third andfourth electrodes are placed in a predetermined arrangement with respectto each other wherein the arrangement is adapted to fit around a pipe ortube; where the plurality of capacitance segments of the second, thirdand fourth electrodes are individually addressable with voltages; wherethe capacitance segments of each of the first, second, third, and fourthelectrodes may be paired with corresponding capacitance segments fromthe other electrodes to form capacitors; and where the capacitors may beconnected to a measuring circuit and wherein the capacitors inducecurrents in the measuring circuit when charged, the current used toobtain capacitance levels of the capacitors.

An electrical capacitance tomography system for use with the sensor ofthe present invention is comprised of an image reconstruction processorin communication with the measuring circuit for providing an image ofthe area between the first, second, third and fourth electrodes based ondata collected from the measuring circuit.

In another embodiment, the ECVT system of the present invention may beused in conjunction with humans and animals to detect fluid/object flowand different tissues through the body of humans and animals. In such anembodiment, the sensors of the present invention can be place around ahuman or animal (fully or partially) to detect fluid/object flowaccording to the principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In addition to the features mentioned above, other aspects of thepresent invention will be readily apparent from the followingdescriptions of the drawings and exemplary embodiments, wherein likereference numerals across the several views refer to identical orequivalent features, and wherein:

FIG. 1 illustrates one example of a conventional circuit for measuringcapacitance.

FIG. 2 illustrates one example of an adaptive capacitance plate(electrode) of the present invention.

FIGS. 3A and 3B illustrate example electric field distributions foropposite plates of a traditional ECVT sensor.

FIGS. 4A and 4B illustrate example electric field distributions foropposite plates of an adaptive ECVT sensor.

FIGS. 5A and 5B illustrate cross-sectional views of electric fielddistribution for traditional and adaptive sensor, respectively.

FIG. 6 illustrates one example embodiment of a capacitance measuringcircuit for the adaptive sensors of the present invention.

FIG. 7 illustrates another example embodiment of a capacitance measuringcircuit for the adaptive sensors of the present invention.

FIG. 8 illustrates another example embodiment of a capacitance measuringcircuit for the adaptive sensors of the present invention.

FIG. 9 illustrates another example embodiment of a capacitance measuringcircuit for the adaptive sensors of the present invention.

FIG. 10 illustrates one embodiment of adaptive electrode sensors of thepresent invention.

FIG. 11 illustrates one embodiment of adaptive electrode sensors shownin one example arrangement.

FIGS. 12A and 12B illustrate top cross-sectional views of electric fielddistributions for two example embodiments.

FIGS. 13A and 13B illustrate isosurface views of electric fielddistributions for two example embodiments at the 50 v/m level.

FIGS. 14A and 14B illustrate isosurface views of electric fielddistributions for two example embodiments at the 75 v/m level.

FIG. 15 illustrates another example arrangement of adaptive sensorplates of the present invention.

FIGS. 16A and 16B illustrate top cross-sectional views of electric fielddistributions for two additional example embodiments.

FIGS. 17A and 17B illustrate isosurface views of electric fielddistributions for two additional example embodiments at the 50 v/mlevel.

FIGS. 18A and 18B illustrate isosurface views of electric fielddistributions for two additional example embodiments at the 75 v/mlevel.

FIG. 19 illustrates an example embodiment of a capacitance measuringcircuit for adaptive sensors of the present invention.

FIG. 20 illustrates an example embodiment of capacitance platesactivated by different voltage levels through voltage dividers.

FIG. 21 illustrates an example circuit design when voltage control is inan acquisition box.

FIGS. 22A, 22B and 22C illustrate an example of using adaptive platesfor a conventional ECVT sensor.

FIGS. 23A and 23B illustrate example voltage distributions for one platein a conventional and adaptive ECVT sensor, respectively.

FIGS. 24A and 24B illustrate average sensitivity along the verticaldirection of a conventional ECVT and adaptive ECVT sensor, respectively,for the example shown in FIGS. 23A and 23B.

FIGS. 25A and 25B illustrate another example of voltage distributionsfor one plate in a conventional and adaptive ECVT sensor; respectively.

FIGS. 26A and 26B illustrate average sensitivity along the verticaldirection of a conventional ECVT and adaptive ECVT sensor, respectively,for the example shown in FIGS. 25A and 25B.

FIGS. 27A and 27B illustrate another example of voltage distributionsfor one plate in a conventional and adaptive ECVT sensor, respectively.

FIGS. 28A and 28B illustrate average sensitivity along the verticaldirection of conventional ECVT and adaptive ECVT sensor, respectively,for the example shown in FIGS. 27A and 27B.

FIGS. 29A, 29B and 29C illustrate the feasibility of combining differentvoltage distributions to provide desired focus and steering for higherimage resolution.

FIGS. 30A, 30B and 30C are isosurface reconstruction results forsimulated capacitance data of an example shape.

FIGS. 31A, 31B and 31C are vertical sliced reconstruction results forsimulated capacitance data of an example shape.

FIG. 32 illustrates another example embodiment of a capacitancemeasuring circuit for adaptive sensors of the present invention.

FIG. 33 illustrates an example circuit design when voltage control is inadaptive sensor side or when the voltage is distributed using componentsout of the acquisition box and where a conventional measuring circuitcan be used to acquire capacitance signals of the adaptive sensor.

FIG. 34 illustrates an example circuit design with its equivalentrepresentation when voltage control is in adaptive sensor side.

FIG. 35 illustrates an example diagram of a ECVT system.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

The following detailed description of the example embodiments refers tothe accompanying figures that form a part thereof. The detaileddescription provides explanations by way of exemplary embodiments. It isto be understood that other embodiments may be used having mechanicaland electrical changes that incorporate the scope of the presentinvention without departing from the spirit of the invention.

As depicted in FIGS. 1A and 1B of U.S. Patent Application PublicationNo. U.S. 2010/0097374 referenced herein, an array of electrodes (e.g.,capacitance plates) are arranged to form a capacitance sensor. In oneapplication, this sensor may be placed around a pipe or vent to detectmovement within the receptacle to provide imaging data. In aconventional ECVT system, the sensor is made up of capacitance plateswhere the capacitance is measure between a selected pair of plates. Theprinciple of the basic measuring circuit involves connecting one plate(source electrode or sending electrode) of the sensor to a voltage(e.g., Vi) and another plate (detecting electrode or receivingelectrode) to a capacitance measurement circuit. FIG. 1 illustrates oneexample of a conventional circuit 10 for measuring capacitance. Cx shownat 12 represents the capacitor formed from the selected source anddetecting electrode. The portion of the circuit to the right of Cx isthe basic capacitance measuring circuit. In one embodiment, the voltagesource Vi and capacitance measuring portion of the circuit 16 areconnected to the source and detecting electrodes, respectively, usingCMOS switches. In a typical operating cycle, the capacitor Cx is chargedto voltage Vi and then is discharged which causes current to flow intothe capacitance measurement portion of the circuit. At least a portionof the current generated flows through the operational amplifier 18. Theoutput voltage Vo is related to the value of the resistor Rf 20 andcapacitor Cf 22 (see formula referenced in FIG. 1). In one embodiment,the capacitance is measured between all of the plates (selecting twoplates at a time) of the sensor array and the data collected is used toreproduce an image of the multiphase flow between the sensors.

FIG. 2 illustrates one example of an adaptive capacitance plate(electrode) 24 of the present invention. In this example, the electrodesof the sensor array are comprised of a plurality of smaller plates orsegments 26 (e.g., smaller capacitance plates or electrodes) which canbe individually addressed. The shape of the capacitance segments can bemade up various shapes where each plate can be activated with the sameor different voltages, frequencies, or phase shifts. Segments of eachelectrode are preferably connected together in parallel, with voltagecontrol applied independently to each segment. Segments of interestchosen to form sender or receiver plates can be activated by electronicswitches that open or close to connect a particular segment in parallelwith others chosen in same plate.

In a conventional ECVT sensor, each plate is activated by equal voltagedistribution or a voltage distribution “envelope.” In a preferredembodiment, “envelope” means the shape of the voltage distributionapplied to the plate or capacitance segments. Changing of the envelopeapplied to the capacitance segments of a plate allows control oversensor sensitivity and allows focusing of the sensor. Some of the waysto change the envelope is to change the frequency of the appliedvoltage, change the voltage applied, or change the phase of thefrequency applied. The following description will demonstrate exampleapplications and features of an adaptive ECVT by applying differentenvelopes on each plate. This is preferably achieved by dividing eachplate into small segments and distributing voltage according theenvelope. These examples demonstrate how to focus and provide 3Dsensitivity of each adaptive ECVT sensor with different envelopes. Inone embodiment, focus may be achieved by changing envelope frequency. Inone embodiment of the invention, change of envelope phase shift changessensitivity distribution.

FIGS. 3A and 3B illustrate example electric field distributions foropposite plates of a traditional ECVT sensor. As illustrated, theelectric field is generally stronger at the edges and weaker toward thecenter. The sensitivity matrix from such a distribution is generallyill-conditioned.

FIGS. 4A and 4B illustrate example electric field distributions foropposite plates of an adaptive ECVT sensor. In the preferred embodiment,the voltage on the plates follows a 2D sine function. As illustrated,the electric field is generally stronger towards the center and moreuniform throughout the imaging area.

FIGS. 5A and 5B illustrate example cross-sectional views of electricfield distribution for traditional and adaptive sensors, respectively.In this example, the adaptive sensor is used with a 2D sine distributionwith the same amplitude as the traditional sensor of FIG. 5A. The moreuniform distribution of electric field of the adaptive sensor willprovide higher image resolution.

FIGS. 22A, 22B and 22C provide an example of using adaptive platesinstead of a conventional ECVT sensor. The adaptive sensor of thepresent invention is preferably comprised of smaller segments thatallows focusing of the sensor. The following figures provide voltage andsensitivity distributions for various examples.

FIGS. 23A and 23B illustrate examples of voltage distributions for oneplate of a conventional ECVT sensor and an adaptive ECVT sensor,respectively. In this example, voltage is applied on the adaptive platesin a shape of half cycle cosine wave along the vertical and horizontaldirection. The period of each cosine is set based on the vertical andhorizontal dimension of each plate, respectively. This shape of voltagedistribution on each plate is referred to as the “envelope.”

FIGS. 24A and 24B illustrate average sensitivity along the verticaldirection of conventional ECVT and adaptive ECVT sensors, respectively,for the example of FIG. 23. The adaptive sensor here has a voltagedistribution as in FIG. 23B. Weak sensitivity zones, where slope oramplitude are near zero, are highlighted.

FIGS. 25A and 25B illustrate example voltage distributions for one platein a conventional and adaptive ECVT sensor, respectively. In thisexample, voltage is applied on the adaptive plates in a shape of a fullcycle cosine wave along the vertical and half cosine cycle along thehorizontal direction. The period of each cosine is set based on thevertical and horizontal dimension of each plate, respectively.

FIGS. 26A and 26B illustrate example average sensitivity along thevertical direction of a conventional ECVT and adaptive ECVT sensor,respectively, for the example of FIGS. 25A and 25B. The adaptive sensorhere has voltage distribution as in FIG. 25B. Weak sensitivity zones,where slope or amplitude is near zero, are highlighted. It isillustrated here, by comparison with FIG. 24, that a change in envelopefrequency results in an increase in the number of high and lowsensitivity zones. This is referred to as focus of adaptive sensorsensitivity or “beams”.

FIGS. 27A and 27B illustrate example voltage distributions for one platein a conventional and adaptive ECVT sensor, respectively. In thisexample, voltage is applied on the adaptive plates in a shape of halfcycle cosine wave along the vertical and horizontal direction,respectively, with a 45 degrees phase shift along the verticaldirection. The period of each cosine is set based on the vertical andhorizontal dimension of each plate, respectively.

FIGS. 28A and 28B illustrate average sensitivity along the verticaldirection of a conventional ECVT and adaptive ECVT sensor, respectively,for the example of FIG. 27. The adaptive sensor here has voltagedistribution as in FIG. 27B, Weak sensitivity zones, where slope oramplitude are near zero, and strong sensitivity zones, where slope andamplitude are high, are also highlighted. It is illustrated here, bycomparison with FIG. 24, that a change in envelope phase results in achange in the location of strong and weak sensitivity locations. This isreferred to as steering of adaptive sensor sensitivity or “beams”.

FIGS. 29A, 29B and 29 are examples that illustrate the feasibility ofcombining different voltage distributions to provide desired focus andsteering for higher image resolution. Average sensitivity along thevertical direction of an adaptive ECVT sensor with a combined envelopeis depicted in FIG. 29C. Here, through a combined envelope voltagedistribution, weak sensitivity zones are eliminated and averagesensitivity is leveled over sensor length.

FIGS. 30B and 30C are example isosurface reconstruction results forsimulated capacitance data of the shape in FIG. 30A Capacitance data wassimulated using a conventional ECVT sensor and an adaptive ECVT sensorwith an envelope as in FIG. 29C. In this example, conventional andadaptive sensors have the same number of plates—twelve. Using adaptivesensors, reconstruction results illustrate better features to theconventional sensor when compared to the original distribution.

FIGS. 31A, 31B and 31C are vertically sliced reconstruction results forsimulated capacitance data of the shape in FIG. 30A. Capacitance datawas simulated using a conventional ECVT sensor and an adaptive ECVTsensor with an envelope as in FIG. 29C. In this example, conventionaland adaptive sensors have the same number of plates—twelve. Usingadaptive sensors, reconstruction results illustrate better features toconventional sensor when compared to the original distribution.

FIG. 6 illustrates one example embodiment of a capacitance measuringcircuit 28 for an adaptive sensor of the present invention. Again, avoltage source Vi 30 is connected to an electrode (source or sendingelectrode) of the adaptive sensor of the present invention. In thisembodiment, a capacitance measurement circuit, shown generally at 32, isconnected to another electrode (detecting or receiving electrode) of theadaptive sensor so that a capacitance measurement can be obtained forthe selected source and detecting electrodes. The capacitors Cx1-Cxn,shown generally at 34, represent the n number of capacitance segments ofthe selected source electrode and the detecting electrode. Asillustrated, each capacitance segment of the electrodes can beindividually addressed by separated voltage sources shown generally at36 (V1-Vn). These voltage sources are used for regulating the voltagelevels and phase shifts on the capacitance segments of each of theelectrodes on the adaptive sensor. The voltage across each of thecapacitor segments (Vxn) is the combination of the voltage source Vi andthe voltage sources connected to each capacitor segment (Vn).Accordingly, using the associated formula as depicted in FIG. 6, themeasured Vo can be used to calculate each of the equivalent capacitance(Cxn) of the capacitance segments of the activated electrode. Theassociated formula is for Cxn=Cx1=Cx2 . . . =Cxi. For segments withdifferent capacitance values, the equivalent capacitance is calculatedusing the formula:

$V_{0} = {\left( \frac{j\;\omega\; R_{f}}{1 + {j\;\omega\; C_{f}R_{f}}} \right)\left( {\sum\limits_{i = 1}^{n}{V_{xi}C_{xi}}} \right)}$

As discussed, in one embodiment, n(n−1)/2 independent mutual capacitancemeasurements are measured and used for image reconstruction. Forexample, the capacitance between each of the electrodes of the sensorare measured in turn and image reconstruction is performed using thiscapacitance data. In other words, capacitance measurements are obtainedfrom every pair or electrode combination of the sensor, in turn, to beused in image reconstruction.

Different amplitudes of voltage can be applied to different capacitancesegments depending on the application and the result desired. Forexample, the greater amplitudes can be applied to the capacitancesegments in the center of the electrodes if it is desired to have moreresolution toward the center of the imaging region. Accordingly,interaction between different activated segments, activated withdifferent amplitudes, would change electric field distribution insidethe imaging domain, providing control over sensor sensitivity. Controlof the electric field distribution would also enable the focusing andzooming of sensor sensitivity to specific imaging regions.

It is appreciated that the voltage sources herein discussed may beconnected to the capacitance segments of each of the electrodes of thesensor array using known switch technologies. Using switches, the systemcan selectively choose which electrodes to activate by connecting thevoltage sources to the selected electrodes through the switches. Inanother embodiment, switching or multiplexing circuit elements can beused to connect the appropriate voltage sources to each of thecapacitance segments of the selected electrode allowing various elementsto be selectively connected to each capacitance segment depending on thefocus and sensitivity desired. For example, voltage sources of greateramplitude may be switched or connected to the capacitance segments inthe center of the electrode or imaging domain so as to focus themeasurements towards the center of the electrode or imaging domain.

In an alternate embodiment, instead of using different amplitudes,different frequencies may be used to activate electrode segmentsenabling concurrent measurements of different capacitance valuesintroduced by electric field beams of different frequencies. In yetanother alternate embodiment, different phase shifts may be used toactivate electrode segments enabling steering of the electric fieldinside the imaging domain.

In the preferred embodiment, adaptive ECVT technology of the presentinvention enables increasing capacitance measurements without reducingsignal to noise ratio. Adaptive ECVT technology allows a large number ofcapacitance measurements by connecting different segments together andactivating them with different voltage levels. This allows morecapacitance measurement without decreasing noise level (e.g., signalintegrity is preserved). This allows enhanced image quality.

FIG. 7 illustrates another example embodiment of a capacitance measuringcircuit for the adaptive sensors of the present invention. In thisembodiment, other circuit elements shown as A1-An generally at 38, suchas current sources or even passive elements such as resistors,inductors, or capacitors, can be used to regulate the voltages oncapacitors Cx1-Cxn. For example, a voltage divider as shown in FIG. 20can be used to regulate voltages on the individual capacitance segments.

FIG. 8 illustrates another example embodiment of a capacitance measuringcircuit for the adaptive sensors of the present invention where voltagesources, shown as V1 r-Vnr generally at 40, are also applied to each ofthe capacitance segments on the detecting electrode side of the sensorto individually address the segments.

FIG. 9 illustrates another example embodiment of a capacitance measuringcircuit for the adaptive sensors of the present invention where otheractive or passive circuit elements, shown as A1 r-Anr, generally at 42,are also applied to each of the capacitance segments on the detectingelectrode side of the sensor to individually address the segments.

FIG. 10 illustrates one embodiment of adaptive electrode sensors of thepresent invention. In this example, each electrode of the adaptivesensor is made up of four capacitance segments 42 of helical shape. Inone embodiment, a positive voltage can be applied to each of thecapacitance segments of the source electrode 44 and a negative voltagecan be applied to each of the capacitance segments of the detectingelectrode 46. As discussed, different values of voltages applied to thecapacitance segments (Vp1-Vp4; Vn1-Vn4) are used to steer the electricfield and focus on a certain imaging region. In an adaptive ECVT sensor,the sensor is preferably comprised with a plurality of these electrodes,however the example simulation described here is shown using only twoelectrodes (one pair of source and detecting electrodes). It isappreciated that increasing the number of segments in the electrodesgives more flexibility in controlling electric field distribution.Although applied voltages are preferably time varying, they are depictedin the following examples as DC voltages for illustration purposes. Forthe following example illustrated with the example electrodes of FIG.10, capacitance measurements are obtained using the capacitancemeasurement circuit of FIG. 19. As illustrated, capacitance measurements(Cx1-Cxn) are obtained between corresponding segments of the source anddetecting electrodes (e.g., four pairs). Again, by obtaining the voltagemeasurement Vo, and applying the formula set forth in FIG. 8, theequivalent of the capacitances Cx1-Cx4 can be obtained. This data isthen used to reconstruct the image for a multiphase flow between theadaptive sensors.

FIG. 11 illustrates one embodiment of adaptive electrode sensors of FIG.10 shown in one example arrangement. Two different cases are explored:

-   -   Case 1:        -   Vp1=Vp2=Vp3=Vp4=Vp5=+5 volts;        -   Vn1=Vn2=Vn3=Vn4=−5 volts.    -   Case 2:        -   Vp1=+1 v, Vp2=+2 v, Vp3=+4 v, Vp4=+7 v;        -   Vn1==1 v, Vn2=−2 v, Vn3=−4 v, Vn4=−7 v.

With reference to FIG. 19, when these voltages are applied, the voltagedifferences (Vx1-Vxn) between each corresponding segment causes currentsto flow in proportion to the voltage difference and capacitance(Cx1-Cx4) of each segment pair. Accordingly, because largest appliedvoltages in this example are applied to the center capacitance segmentof the electrodes, the largest current will most likely flow from Cx4.Each of the currents flowing from the capacitance segments are combinedto form I1 shown generally at 48. In the preferred embodiment, a smallportion of current I1 will go to the operational amplifier (current I3)and the rest will flow to Rf and Cf (current I2). The output voltage Vowill be related to the values of Rf and Cf and the level of current. Itis appreciated that changing the shape of the capacitance segments orchanging the voltages applied, and the distributions thereof, thecurrent and the output voltage will change accordingly.

As discussed, the electric field intensity, and therefore capacitancesensitivity, will be higher in the imaging region where the appliedvoltage difference is the greatest. In this example, the greatestvoltage difference occurs between the center capacitance segments (Vx4).When an object is present between the activated source and detecting(i.e., sender and receiver, respectively) electrodes, the measurecapacitance will change based on the relative electric field intensityat the object location. Accordingly, in this example, objects passingthrough the middle of the sensor will generate a greater change incapacitance due to the higher sensitivity. The change in capacitance dueto the object will result in an increase in total current I1 inproportion to the change in capacitance levels. Because the outputvoltage Vo depends on total current I1, the output voltage will alsochange proportional to the change in current. This measured change inoutput voltage can be used to calculate the change in capacitance levelsbetween the capacitance segments which are then used to reconstructvolume images of objects or materials between the sensors.

According to principles of the present invention, the electric field canbe concentrated at a location where higher sensitivity is desired. Theelectric field can also be controlled toward smoother gradients for moreaccurate information.

FIGS. 12A and 12B illustrate top cross-sectional views of electric fielddistributions for two example embodiments. FIGS. 13A and 13B illustrateisosurface views of electric field distributions for two exampleembodiments at the 50 v/m level. FIGS. 14A and 14B illustrate isosurfaceviews of electric field distributions for two example embodiments at the75 v/m level. FIGS. 12-14 depict variation in electric fieldconcentration resulting from applying different voltage levels toindividual segments. In this particular example, electric field is morefocused toward edges of plates and center of imaging region.

FIG. 15 illustrates another example arrangement of adaptive sensorelectrodes of the present invention. In this example the electrodes areplaced in adjacent to each other.

-   -   Case 3:        -   Vp1=Vp2=Vp3=Vp4=Vp5=+5 volts;        -   Vn1=Vn2=Vn3=Vn4=−5 volts.    -   Case 4:        -   Vp1=+1 v, Vp2=+3 v, Vp3=+5 v, Vp4=+7 v;        -   Vn1==1 v, Vn2=−3 v, Vn3=−5 v, Vn4=−7 v.

FIGS. 16A and 16B illustrate top cross-sectional views of electric fielddistributions for two additional example embodiments of FIG. 15. Asillustrated the electric field gradient, moving between plates in thedirection of the arrow, is more visible in Case 4.

FIGS. 17A and 17B illustrate isosurface views of electric fielddistributions for two additional example embodiments at the 50 v/mlevel. FIGS. 18A and 18B illustrate isosurface views of electric fielddistributions for two additional example embodiments at the 75 v/mlevel. As illustrated, the figures illustrate that the electric field ismore focused for Case 4.

FIG. 19 and FIG. 32 illustrate example embodiments of a capacitancemeasuring circuit for adaptive sensors of the present invention aspreviously discussed. FIG. 20 illustrates an example embodiment ofcapacitance plates activated by different voltages levels throughvoltage dividers.

FIG. 21 depicts an example circuit design when voltage control is froman acquisition box, before connecting cables to the sensor segments.Typically, when measuring capacitance for tomography imaging, thevariation in the signal due to change in material density ordistribution in the imaging domain is measured. Usually the range ofthis change is minimal compared to static capacitance that exist in thesystem. In order to focus the measuring circuit on that varyingcomponent only (yielding accurate measurements), it is preferable toeliminate any static capacitance that is often referred to as “Parasiticcapacitance”. Without eliminating it, the resolution of the circuit willtypically be stretched over a very wide range, instead of being focusedon that small variable part. Cables that connect the circuit to thesensors are a major component of this static “parasitic capacitance”.The circuit of FIG. 21 is different in the sense that it includesvertical branches of capacitance (Cp1 and Cp2 that are staticcapacitance mainly introduced by cables) after the voltage sources ofindividual segments. Accordingly, controlling voltages for each segmenthappen before the cable (at the main circuit or acquisition boxlocation). The circuit as it is structured, automatically eliminatesmost of the static capacitance and the output voltage depends on Cxwithout regard to Cp1 or Cp2.

FIG. 33 illustrates an example circuit design when voltage control is inadaptive sensor side. In such an arrangement, a conventional measuringcircuit may be used to measure adaptive capacitance. Voltagedistribution on segments and adaptive capacitance value are determinedby passive or active elements connected to the plate segments,preferably outside of the acquisition box. FIG. 34 illustrates anexample circuit design with its equivalent representation when voltagecontrol is in adaptive sensor side. Voltage division is based on totalcapacitance for each segment Ci_total (including parasitic) and R:

-   For Ri1+Ri2>>jwCxi and Ri1+Ri2˜=1/jwCi_total:-   i=Vi(jwCi_total)/(1+RjwCi_total)-   Vxi=i/jwCxi, voltage is stable for Cxi>>Ci_total    The equivalent circuit representations relate the capacitance    measured by a conventional circuit to the total capacitance of an    adaptive sensor when voltage distribution is achieved outside the    box.

FIG. 35 illustrates an example diagram of an ECVT system.

While certain embodiments of the present invention are described indetail above, the scope of the invention is not to be considered limitedby such disclosure, and modifications are possible without departingfrom the spirit of the invention as evidenced by the following claims:

What is claimed is:
 1. A system for tomographic imaging of a domain in apipe, tube or object, the system comprising: a sensor, comprising: aplurality of electrodes configured to be placed around the pipe, tube orobject, each electrode comprising a plurality of capacitance platesegments; and a voltage source; a measurement circuit electricallycoupled to the sensor; wherein the plurality of electrodes is comprisedof: a first electrode, having a plurality of capacitance plate segmentsthat are addressable with the voltage source; a second electrode, havinga plurality of capacitance plate segments, the capacitance platesegments of the second electrode electrically coupled to the measurementcircuit; and wherein the capacitance plate segments of the firstelectrode form capacitance pairs with at least one of the capacitanceplate segments of the second electrode when activated; and wherein thesystem is adapted to collect capacitance data by: defining a capacitorby using a capacitance plate segment on the first electrode as a sourceelectrode, using a capacitance plate segment on the second electrode asa detecting electrode, charging and discharging the defined capacitor bydirecting a predetermined voltage to the source electrode from thevoltage source; detecting a capacitance of the defined capacitor bydetecting a current induced in the detecting electrode; an imagereconstruction processor, in communication with the measurement circuit,wherein the image reconstruction processors is adapted to convertdetected capacitance data into an image; and wherein the system isadapted to activate various combinations of electrodes with differentvoltage distributions or envelopes to provide control of systemsensitivity.
 2. The system of claim 1, wherein the measurement circuitis adapted to receive current from a plurality of the capacitance pairsof the first and second electrodes and convert it to an output voltage(Vo).
 3. The system of claim 2, wherein the image reconstructionprocessor is programmed with one or more software routines executing onthe processor to determine volume images from the output voltage (Vo).4. The system of claim 1, wherein the measurement circuit is comprisedof: an operational amplifier circuit adapted to receive current from aplurality of the capacitance pairs of the first and second electrodesand convert it to an output voltage (Vo).
 5. The system of claim 4,wherein the output voltage (Vo) is a signal having an amplitude, phase,and frequency and wherein the processor is programmed with one or moresoftware routines executing on the processor to determine thecapacitance between the first and second electrodes.
 6. The system ofclaim 1, further comprising a plurality of switches electricallyconnected to the voltage source and the plurality of capacitance platesegments of the first electrode for selectively activating each of theplurality of capacitance plate segments of the first electrode.
 7. Thesystem of claim 1, wherein the system is adapted to control thesensitivity of the sensor by changing the frequency of the voltagedistribution applied to at least one electrode.
 8. The system of claim1, wherein the system is adapted to activate one electrode at a time asa source electrode and one electrode as the detecting electrode, andwherein the detecting electrode is connected to the measurement circuit.9. The system of claim 1, wherein the image reconstruction processor isadapted to obtain the capacitance between all the electrodes andreconstruct an image of the region between the electrodes based on thecapacitances obtained.
 10. The system of claim 1, wherein a switchcontrolled by the measurement circuit selectively connects eachcapacitance plate segment of each electrode to the voltage source. 11.The system of claim 1, wherein the system is adapted to focus theelectric field between the first and second electrodes by means of thevoltage levels used to address the capacitance plate segments.
 12. Thesystem of claim 1, wherein sensor sensitivity is controlled by varyingthe voltage distribution or envelope applied to the capacitance platesegments.
 13. The system of claim 1, wherein the electric field betweenelectrodes of the sensor is focused toward the center of the electrodesby connecting voltages of various amplitudes to the capacitance platesegments of at least one of the electrodes, and wherein the voltagesconnected towards the center of the electrode is greater than thevoltages connected to the periphery of the electrode.
 14. The system ofclaim 1, wherein the sensor is adapted to be placed around a body of ahuman or animal to detect fluid flow or tissues through the body of thehuman or animal.
 15. The system of claim 1, wherein the measurementcircuit is adapted to receive current from all of the capacitance pairsof the first and second electrodes and convert it to an output voltage(Vo); wherein the processor is programmed with one or more softwareroutines executing on the processor to determine images from the outputvoltage (Vo); wherein each of the capacitance plate segments of each ofthe first electrode are individually addressable by voltages and wheresensor sensitivity is controlled by varying the voltage distribution orenvelope applied to the capacitance plate segments of the firstelectrode.
 16. The system of claim 1, wherein the system is adapted toallow control of sensitivity of the system by changing the phase of thevoltage distribution applied to the first electrode.
 17. The system ofclaim 1, wherein an envelope shape applied to the first electrode can bea combination of different envelopes to control steering or focus ofsystem sensitivity toward a desired region.
 18. The system of claim 1,wherein the system is adapted to allow for an increase in the number ofindependent capacitance measurements by using different envelopes foractivating electrodes, and wherein each envelope has a differentsensitivity distribution.
 19. The system of claim 1, wherein the systemis adapted to allow for an increase in the number of independentcapacitance measurements by selecting different capacitance platesegments of an electrode to activate each time a capacitance measurementis acquired.
 20. The system of claim 1, wherein the physical dimensionsof the sensor are increased by adding electrodes or capacitance platesegments to the sensor.
 21. The system of claim 1, wherein all thecapacitance plate segments of the second electrode are electricallycoupled to the measurement circuit.
 22. A system for tomographic imagingof a domain in a pipe, tube or object, the system comprising: a sensor,comprising: a plurality of electrodes configured to be placed around thepipe, tube or object, each electrode comprising a plurality ofcapacitance plate segments; and a voltage source; a measurement circuitelectrically coupled to the sensor; wherein the plurality of electrodesis comprised of: a first electrode, having a plurality of capacitanceplate segments that are addressable with the voltage source; a secondelectrode, having a plurality of capacitance plate segments, thecapacitance plate segments of the second electrode electrically coupledto the measurement circuit; and wherein the capacitance plate segmentsof the first electrode form capacitance pairs with at least one of thecapacitance plate segments of the second electrode when activated; andwherein the system is adapted to collect capacitance data by: defining acapacitor by using a capacitance plate segment on the first electrode asa source electrode, using a capacitance plate segment on the secondelectrode as a detecting electrode, charging and discharging the definedcapacitor by directing a predetermined voltage to the source electrodefrom the voltage source; detecting a capacitance of the definedcapacitor by detecting a current induced in the detecting electrode; animage reconstruction processor, in communication with the measurementcircuit, wherein the image reconstruction processors is adapted toconvert detected capacitance data into an image; and wherein themeasurement circuit is adapted to receive current from all of thecapacitance pairs of the first and second electrodes and convert it toan output voltage (Vo); wherein the image reconstruction processor isprogrammed with one or more software routines executing on the processorto determine images from the output voltage (Vo); wherein each of thecapacitance plate segments of each of the first electrode areindividually addressable by voltages and where sensor sensitivity iscontrolled by varying the voltage distribution or envelope applied tothe capacitance plate segments of the first electrode; and wherein thesystem is adapted to activate various combinations of electrodes withdifferent voltage distributions or envelopes to provide control ofsystem sensitivity.
 23. A system for tomographic imaging of a domain ina pipe, tube or object, the system comprising: a sensor, comprising: aplurality of electrodes configured to be placed around the pipe, tube orobject, each electrode comprising a plurality of capacitance platesegments; and a current source; a measurement circuit electricallycoupled to the sensor; wherein the plurality of electrodes is comprisedof: a first electrode, having a plurality of capacitance plate segmentsthat are addressable with the current source; a second electrode, havinga plurality of capacitance plate segments, the capacitance platesegments of the second electrode electrically coupled to the measurementcircuit; and wherein the capacitance plate segments of the firstelectrode form capacitance pairs with at least one of the capacitanceplate segments of the second electrode when activated; and wherein thesystem is adapted to collect capacitance data by: defining a capacitorby using a capacitance plate segment on the first electrode as a sourceelectrode, using a capacitance plate segment on the second electrode asa detecting electrode, charging and discharging the defined capacitor bydirecting a predetermined current to the source electrode from thecurrent source; detecting a capacitance of the defined capacitor bydetecting a current induced in the detecting electrode; an imagereconstruction processor, in communication with the measurement circuit,wherein the image reconstruction processors is adapted to convertdetected capacitance data into an image; and wherein the system isadapted to activate various combinations of electrodes with differentvoltage distributions or envelopes to provide control of systemsensitivity.
 24. The system of claim 23, wherein the measurement circuitis adapted to receive current from a plurality of the capacitance pairsof the first and second electrodes and convert it to an output voltage(Vo).
 25. The system of claim 24, wherein the image reconstructionprocessor is programmed with one or more software routines executing onthe processor to determine volume images from the output voltage (Vo).26. The system of claim 23, wherein the measurement circuit is comprisedof: an operational amplifier circuit adapted to receive current from aplurality of the capacitance pairs of the first and second electrodesand convert it to an output voltage (Vo).
 27. The system of claim 26,wherein the output voltage (Vo) is a signal having an amplitude, phase,and frequency and wherein the processor is programmed with one or moresoftware routines executing on the processor to determine thecapacitance between the first and second electrodes.
 28. The system ofclaim 23, further comprising a plurality of switches electricallyconnected to the current source and the plurality of capacitance platesegments of the first electrode for selectively activating each of theplurality of capacitance plate segments of the first electrode.
 29. Thesystem of claim 23, wherein the system is adapted to control thesensitivity of the sensor by changing the frequency of the voltagedistribution applied to at least one electrode.